My triangles are all messed up. Then the mistake boiled down to this piece of code
//6. bottom-triangles
//b1, b4, f3
1,-1,1, -1,-1,1 -1,-1,0,
//b1, f3, f4
1,-1,1, -1,-1,0, 1,-1,0
Compiler is fine. Just my triangle! Can you spot the mistake! it is a fun mistake.